Sweet looking place! Do I spy a downstairs concrete-floored tank room??!! :thup:
I think as Smidey said the only thing to worry about is how clean the water tank and gutters are. First thing to do is to test the water, but I'm guessing it will be fine (I was using roof water for my tank while staying at Mum&Dads and despite their cat crapping all over the roof the water in the tank still had no detectable ammonia/nitrite/nitrate). Rain water is very soft tho, and you may need to use crushed shell/coral to help buffer, and/or dose with calcium/baking soda etc during water changes. Can nearly be treated the same as RO water, water from my tank has around 6ppm TDS, so virtually nothing!